1. Field of the Invention
The present invention relates to a method for the manufacture of matrix arrangements, such as multi-color light emitting diode displays made from electro-luminescent polymers or low molecular weight luminescent materials (OLED), sensor panels, based on organic conductive materials, and products manufactured using the method,
2. Description of the Related Art
Methods of manufacturing organic polymer light emitting diodes are disclosed in EP 0423283, WO90/13148, and U.S. Pat. No. 5,869,350. Methods of manufacturing organic light emitting diodes based on low molecular weight luminescent materials are disclosed in U.S. Pat. Nos. 4,769,292 and 4,720,432.
Up to now, full-color polymer OLED's were manufactured by printing methods, such as using ink-jet printers. Corresponding methods are described in EP 0940796, EP 0940797, EP 0989778, WO 99/43031, WO 99/66483, WO 98/28946, U.S. Pat. No. 6,087,196, WO 00/12226, and WO 00/19776. In the method of ink-jet printing, a polymer drop is applied for each pixel of a display onto a substrate. The arrangement can be selected in such a way that the polymer drops lie between two electrodes in a common plane or the electrodes and polymer may be superimposed, in which case one electrode is made from a transparent material. With the arrangement of multi-color light emitting pixels in a matrix, a full color OLED screen is subsequently provided.
According to EP 090872, a sensor panel with various types of polymers is produced in the same manner. Polymer drops are jetted by an ink-jet printer between two neighboring microelectrodes on a substrate.
The light-producing efficiency of ink-jetted polymer films is considerably lower than in the case of spin-coated polymer layers. Moreover, there are special requirements for the polymer solution when the ink-jet method is used, such as the use of a high-boiling point solvent, high stability with regard to the drop formation, and good wetting coverage of the substrate surface as well as wetting coverage of the print heads. These requirements mandate complex optimization of existing polymer solutions. In addition, the substrate onto which the polymers are jetted must have pixel cavities into each of which a drop must be placed so that it does not come apart and run into a neighboring pixel cavity. With increasingly higher resolution for screens, increasingly smaller pixel cavities have to be prepared on the substrate, and these smaller pixel cavities are closer to each other than pixel cavities for lower resolution screens. In this case, a physical limit on cavity size is reached depending on the size of the drops of the polymer solution of a certain viscosity and corresponding print head technology. When the limit is exceeded, a drop will inevitably touch the neighboring pixel and the display is then unusable.
The manufacture of full color OLED's on the basis of low molecular weight luminescent materials is achieved by the evaporation of the luminescent materials with the use of shadow masks. This technique is described in U.S. Pat. Nos. 6,153,254 and 5,742,129. In this technique, to produce pixels for the various required colors, e.g., red, green and blue, different types of shadow masks have to be applied and this represents an additional cost factor. During the evaporation process, these shadow masks are subjected to thermal stress and, in addition, they become fouled over a period of time due to the evaporated substances. Thus, this technique requires complex and work-intensive cleaning of the shadow masks and regular replacement of the shadow masks. When using larger shadow masks for larger substrates, gravity represents an additional problem, as the shadow masks tend to sag with the result that the resolution in the middle of the substrate to be coated is no longer ensured.
The application of laser ablation in producing organic light emitting diodes is described in EP 0758192, WO 98/53510 as well as in Noah et al., Applied Physics Letters, Vol. 69, No. 24, 1996, pp. 3650-3652. With the application of laser ablation, OLED's can be manufactured with a stacked layer sequence of anode, light emitting layer, and cathode. In this case, a transparent anode layer is applied to a transparent substrate, and then onto this anode layer a correlated light emitting layer and a metallic cathode layer are sequentially applied. With a laser, the cathode layer and the light emitting layer are divided into separate pixels. The method is only suitable for the manufacture of individual OLED's or mono-color OLED displays, since they have a single type of light emitting layer of the same kind.